>>23319250
>If they didn't explain it in the show it may as well be fanfiction to me
The show had scenes telling you to watch the movie though, like when Eijiro finds a picture of Tsukasa leaving his sister and comments on it having the aura of a family.

That said, the movie itself is kind of messy, so if you don't like Decade I doubt All Riders vs Dai-Shocker would change your mind.